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Title: Hydrochemical and isotopic fingerprinting of the Walloon coal measures and adjacant aquifiers in the Clarence-Moreton and Eastern Basins in Southeast Queensland
Authors: Raiber, M
Cendón, DI
Feitz, A
Sundaram, B
Suckow, A
Keywords: Coal
New South Wales
Coal seams
Sedimentary basins
Issue Date: 7-Jul-2014
Publisher: Geological Society of Australia
Citation: Raiber, M. Cendón, D., Feitz, A., Sundaram, B., & Suckow. A., (2014). Hydrochemical and isotopic fingerprinting of the Walloon coal measures and adjacant aquifiers in the Clarence-Moreton and Eastern Basins in Southeast Queensland. Paper presented at the Australian Earth Sciences Convention 2014, Newcastle NSW, AESC 2014. 22nd Geological Convention, 7-10 July.
Abstract: The Clarence-Moreton and the Surat basins in Queensland and northern New South Wales contain the coal-bearing sedimentary sequences of the Jurassic Walloon Coal Measures, composed of up to approximately 600 m of mudstone, siltstone, sandstone and coal. In recent years, the intensification of exploration for coal seam gas (CSG) resources within both basins has led to concerns that the depressurisation associated with future resource development may have adverse impacts on water resources in adjacent aquifers. In order to identify the most suitable tracers to study groundwater recharge and flow patterns within the Walloon Coal Measures and their degree of connectivity with over- or underlying formations, samples were collected from the Walloon Coal Measures and adjacent aquifers in the northern Clarence-Moreton Basin and eastern Surat Basin, and analysed for a wide range of hydrochemical and isotopic parameters. Parameters that were analysed include major ion chemistry, δ13C–DIC, δ18O, 87Sr/86Sr, Rare Earth Elements and Yttrium (REY), 14C, δ2H and δ13C of CH4 as well as concentrations of dissolved gases (including CH4). Dissolved CH4 concentrations range from below the reporting limit (10 μg/L) to approximately 50 mg/L in groundwaters of the Walloon Coal Measures. However, the high degree of spatial variability of methane concentrations highlights the general complexity of recharge and groundwater flow processes, especially in the Laidley Sub-Basin of the Clarence-Moreton Basin, where numerous volcanic cones penetrate the Walloon Coal Measures and may form pathways for preferential recharge to the Walloon Coal Measures. Interestingly, dissolved CH4 was also measured in other sedimentary bedrock units and in alluvial aquifers in areas where no previous CSG exploration or development has occurred, highlighting the natural presence of CH4 in different aquifers. Radiocarbon ages of Walloon Coal Measure groundwaters are also highly variable, ranging from very young (~82 pMC) to very old (0.43 pMC). While groundwaters sampled in close proximity to the east and west of the Great Dividing Range are mostly young, suggesting that recharge to the Walloon Coal Measures occurs through the basalts of the Great Dividing Range; there are otherwise no clearly discernable spatial patterns and no apparent relationships with depth or distance along inferred flow paths in the Clarence-Moreton Basin. 177 In contrast to this strong spatial variability of CH4 concentrations and groundwater ages, REY patterns and 87Sr/86Sr isotope ratios of Walloon Coal Measure groundwaters appear to be very uniform and clearly distinct from groundwaters contained in other bedrock units. This difference is attributed to the different source material of the Walloon Coal Measures (mostly basalts in comparison to other bedrock units which are mostly composed of mineralogically more variable Paleozoic basement rocks of the New England Orogen). This study suggests that REY and 87Sr/86Sr ratios may be suitable tracers to study the hydraulic connectivity of the Walloon Coal Measures with over- or underlying aquifers, although more studies on the system are required. In addition, this study also highlights the need to conduct detailed water chemistry and isotope baseline studies prior to the development of coal seam gas resources in order to differentiate between natural background values of CH4 and potential impacts of coal seam gas development.
Gov't Doc #: 9552
ISSN: 0729 011 X
Appears in Collections:Conference Publications

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